Kill oracle session in OS LEVEL

Sometimes, “ALTER SYSTEM KILL SESSION” will not terminate a session, it will just mark it as “killed”. In this case you can kill the process or thread of that session at the operation system level.

In Windows

C:\ ORAKILL ORACLE_INSTANCE THREAD;

THREAD means SPID of the process .

We can simply find out THREAD(SPID) By below query.
select spid, osuser, s.program from
v$process p, v$session s where p.addr=s.paddr
Identify SPID of the particular user which you want to Kill

SQL> select spid, osuser, s.program from
v$process p, v$session s where p.addr=s.paddr;

Example

SQL> select spid, osuser, s.program from
v$process p, v$session s where p.addr=s.paddr;

SPID OSUSER PROGRAM
------------------------ ------------------------------ --------------------
8876 NICE JDBC Thin Client

In this above Example THREAD(SPID) is 8876

SQL> Select instance_name from v$instance;
INSTANCE_NAME
-------------
ORCL
C:\ ORAKILL ORCL 8876;

To kill the session on the Unix operatin system, you can use “kill” command:

KILL THREAD

In the above Example

Example : KILL 8876

If after a few minutes the process hasn’t stopped, you can force the session to terminate by using “-9″ parameter:
kill -9 THREAD
Example : KILL -9 8876
Note: Make sure that you are not killing background processes of Oracle such as DBWR, LGWR, SMON, PMON. If you kill one of them, Oracle will crash or become unstable